The clinical treatment of open angle glaucoma is usually based solely or predominately on the presence of characteristic visual field defects. Since the progression of these defects can usually be halted but only rarely reversed by controlling intraocular pressure, their early detection is often the key to successful treatment. Visual field tests for glaucoma are usually limited to achromatic incremental sensitivity (i.e., conventional kinetic and static perimetry). Spatio-temporal variables, brightness, color and adaptation have all been relatively ignored. There are recent indications, however, that tests of these variables can sometimes reveal glaucomatous defects at earlier stages than incremental sensitivity. We propose a systematic psychophysical study of visual function in glaucoma and ocular hypertension. The study will include tests of spatial and temporal resolution, color discrimination and brightness matching, as well as sensitivity comparisons at different adaptation levels. Positions immediately above and below the nasal horizontal meridian will be compared to exploit the "nasal step" pattern of the glaucomatous visual field. We expect these tests, either singly or in conjuction, to (1) reveal glaucomatous visual defects at significantly earlier stages than conventional perimetry and (2) provide clues to the neural mechanisms of glaucomatous visual defects.